The present invention concerns a press section in a paper machine and a structural frame for the same, which comprises, in a direction of running of a paper web therethrough, first a front frame and then a rear frame. Press rolls are mounted on the front and rear frames which form a press roll combination, in which press fabric or fabrics are passed through nips formed between the press rolls.
In prior art compact press sections of a paper machine, such as the Valmet so-called Sym-press (TM) press section, there are horizontal beams above the press rolls both at the servicing side and at the operating side of the paper machine, which connect the front frame and the rear frame of the press section permanently together. In this connection, and also in the following description, the front frame means the frame part that is situated in the direction of running of the web at a front side of the press roll combination, to which, e.g., a suction roll of the press is fixed. In a corresponding manner, the rear frame means the frame part situated at the rear side of the press roll combination.
Difficulties have occurred with respect to replacement both of press fabric and of press rolls in connection with the prior art frame parts of the press sections. These problems have increased with the increase in width of paper machines, in particular due to the fact that the press rolls have become increasingly longer and heavier. For example, a central roll of rock may weigh 70,000 kgs. These problems have also been increased by the fact that press fabrics which are made of plastic material and which are rigid in a transverse direction, have started being used more increasingly. Such press fabric cannot be jammed into a bundle.
Beloit Corporation has attempted to solve these problems described above by means of a so-called "Flip-Top" (trademark of Beloit Corporation) frame construction in which a top frame is used that is provided with a pivot shaft parallel to a transverse direction of the paper machine and situated above the press rolls, whereby either a top part of the front frame or a top part of the rear frame can be opened around the pivot shaft. The two top parts of the frame cannot be opened at the same time.
By opening the top part of the front frame, it is possible to facilitate replacement of the pick-up fabric of the press section and the replacement of the fabric that usually acts as the press fabric in the first nip and in the second nip. The top part of the rear frame is locked thereat as a frame part on whose support the opening-"dumping" o the top part of the front frame takes place. Correspondingly, when the top part of the front frame is in the closed-locked position, the top part of the rear frame can be "dumped" so that the press fabric of a third press nip can be replaced.
The lower fabric of the first nip, which principally runs in a basement space, is replaced by means of arrangements known in and of themselves. The above-noted "Flip-Top" solution can be characterized as a sort of "drawbridge" which is opened around an articulated joint placed expressly at a middle of the bridge, while only one half of the bridge can be opened at a time.
Frame constructions for press sections are known from the Valmet Finnish Patent Applications Nos. 844693 and 854959, in which the front frame and the rear frame are connected to each other and/or to an intermediate frame of the central roll in the press by means of various openable and closeable intermediate frames placed above. Such massive and openable/closeable intermediate frames are usable in and of themselves, but they increase the cost of manufacture of the frame section because relatively massive frame components must be provided with articulated joints and with strong means for opening and closing.
When press roll arrangements with several nips are used, problems of space are also encountered because several different press rolls with the auxiliary devices must be accommodated in a relatively limited space. This is why it has been necessary to place the frame parts that connect the front frame and the rear frame to each other or to an intermediate frame with their opening and closing means in highly congested spaces, which results in problems both in construction and in operation.